1. Field of the Invention This invention relates to read/write magnetic transducers, and relates more particularly to such transducers employing MR or Hall effect read elements.
2. Description of the Prior Art
Thin film magnetic heads or transducers may employ separate elements for recording and reading data. As is well known, thin film magnetic write heads comprise a first magnetic layer, designated as P1, and a second magnetic layer, designated as P2. The P1 and P2 layers make contact at a back closure to form a magnetic yoke having a continuous magnetic path with a write transducing gap between the P1 and P2 layers. During the recording or write mode, electrical signals representative of signals to be recorded are supplied to the transducer and are recorded as magnetic flux signals on an associated surface of a magnetic disk or tape. During the read mode, the recorded magnetic signals are sensed by the read portion of the transducer to produce electrical signals which are read out for further utilization.
It is known that either MR or Hall effect devices may be used as flux sensing elements in thin film heads to implement the readout function. In a conventional recording head having an MR read transducer, the write and read sections of the head must be carefully aligned with each other to effectuate proper track following for writing and reading. The lateral region of sensitivity, which is the read width, is determined by the length of the MR transducer. This transducer length must be approximately equal to the width of the data track to be read. For small track widths, Barkhausen noise is relatively high as compared to signal amplitude because the domain walls that cause such noise are located predominantly at the ends of the MR transducer.
In prior art MR heads, the MR element and a biasing element, which is either a conductor or a magnetic layer, are positioned in a gap formed between two shield elements. An insulating layer that separates the MR element from the shields must be thick enough to insure that there are no pin holes that would cause electrical contact between the shield elements and the MR element.
A further major problem associated with a conventional MR head-is the undesirable generation of thermal noise spikes which occur when the magnetic head makes contact with asperities which protrude from the surface of the magnetic recording medium.
Another problem associated with a conventional MR read head is the generation of a voltage pulse which has a shape similar to that generated by an inductive read head, i.e., the voltage is at a maximum when the magnetization transition is at the center of the sensing gap. In order to detect this point in time with sufficient accuracy, the pulse is differentiated and the zero crossover of the differentiated voltage is detected. This required differentiation causes a substantial decrease in signal-to-noise ratio.
As shown in FIG. 1, the above identified prior art U.S. Pat. No. 5,255,141 discloses one embodiment including magnetic layers P1 and P2 which form a magnetic yoke with a transducing gap G therebetween. A back closure 20 is formed by contact between the ends of layers P1 and P2 to form a continuous magnetic path interrupted by the nonmagnetic transducing gap G. A conductive write coil or winding 10 is embedded in an insulating material 12 which is deposited between layers P1 and P2.
An MR sensor 19 having a defined easy axis of magnetization is provided along the magnetic circuit path in an interspace or well between portions P2A and P2B of the central section of the P2 layer. MR sensor 19 is surrounded by an insulating material 21.
A valve conductor 18 is formed between magnetic layers 14 and 16 which are deposited above the insulating layer 21 and the P2 layer. Layers 14 and 16 are in magnetic contact with the P2 layer, thereby forming a continuous flux path for completing the write magnetic circuit. The valve conductor 18 is formed from one or more copper turns with insulation provided between them and layers 14 and 16. Valve conductor 18 and magnetic layers 14 and 16 form a magnetic valve capable of opening and closing the magnetic shunt path provided by layers 14 and 16.
During the write mode, a track having a width substantially equal to the total width of the transducing gap G is recorded. In the write mode, the valve conductor 18 is not energized so that the signals representing information to be recorded bypass MR element 19 and are directed through the magnetic branches 14 and 16 that surround valve conductor 18. The write signals are transduced at nonmagnetic gap G and recorded on a storage medium.
During the read mode, a current is applied to valve conductor 18 to magnetically saturate layers 14 and 16. When magnetic flux from the recorded medium enters one of the pole tips of the P1 and P2 layers, read element 19 senses the flux as a readout signal as the flux traverses the MR gap. The read efficiency of the head is determined by the ratio of the MR sensor gap length S to valve gap length V.